Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, use a middle or large-sized battery module having a plurality of battery cells electrically connected to each other because high power and large capacity are necessary for the middle or large-sized devices.
Preferably, the middle or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle or large-sized battery module. In particular, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing cost of the pouch-shaped battery is low, and it is easy to modify the shape of the pouch-shaped battery.
In order for the middle or large-sized battery module to provide power and capacity required by a predetermined apparatus or device, it is necessary for the middle or large-sized battery module to be configured to have a structure in which a plurality of battery cells is electrically connected in series to each other, and the battery cells are stable against an external force.
Also, the battery cells constituting the middle or large-sized battery module are secondary batteries which can be charged and discharged. Consequently, a large amount of heat is generated from the high-power, large-capacity secondary batteries during the charge and discharge of the batteries. If the heat, generated from the unit cells during the charge and discharge of the unit cells, is not effectively removed, the heat accumulates in the respective unit cells with the result that the deterioration of the unit cells is accelerated. According to circumstances, the unit cells may catch fire or explode. For this reason, a cooling system is needed in a battery pack for vehicles, which is a high-power, large-capacity battery, to cool battery cells mounted in the battery pack.
In a middle or large-sized battery pack including a plurality of battery cells, on the other hand, the deterioration in performance of some battery cells leads to the deterioration in performance of the entire battery pack. One of the main factors causing the non-uniformity of the performance is the non-uniformity of cooling between the battery cells. For this reason, it is required to provide a structure to secure the uniformity of cooling during the flow of a coolant.
Some conventional middle or large-sized battery packs use a battery pack case configured to have a structure in which a coolant inlet port and a coolant outlet port are located at the upper part and the lower part of the battery pack case such that the coolant inlet port and a coolant outlet port are directed in opposite directions, and the top and bottom of a flow space extending from the coolant inlet port to the battery module are parallel to each other. In this structure, however, a relatively high coolant flux is introduced into flow channels defined between the battery cells adjacent to the coolant outlet port, whereas a relatively low coolant flux is introduced into flow channels defined between the battery cells adjacent to the coolant inlet port with the result that it is difficult to achieve uniform cooling of the battery cells.
In connection with this matter, Korean Patent Application Publication No. 2006-0037600, No. 2006-0037601, and No. 2006-0037627 disclose a middle or large-sized battery pack configured to have a structure in which an air guide plane is inclined downward to a side of a battery pack case opposite to battery cells so that the air guide plane becomes closer to the battery cells with the increase in distance between the air guide plane and a coolant inlet port. Specifically, the air guide plane is inclined at a predetermined angle, for example an angle of 15 to 45 degrees, to the side of the battery pack case opposite to the battery cells, thereby restraining the occurrence of a phenomenon in which a coolant is excessively introduced into flow channels defined between the battery cells adjacent to the coolant outlet port.
However, the inventors of the present application have found that the temperature deviation between the battery cells is high even in the above-described structure with the result that it is not possible to achieve temperature uniformity of a desired level.
Furthermore, in this structure, regions of the air guide plane adjacent to the battery cells may come into contact with the battery cells or the battery module during vibration of the battery pack with the result that noise may be generated from the battery pack or the battery pack may be damaged. Consequently, it is not possible to lower the end of the battery pack case opposite to the coolant inlet port below a predetermined height with the result that it is not possible to design a pack case having optimum temperature deviation.
Meanwhile, in connection with the structure of a conventional battery pack, FIG. 1 is a perspective view illustrating a middle or large-sized battery pack configured to have a structure in which a battery module is mounted in a conventional middle or large-sized battery pack case and FIG. 2 is a vertical sectional view typically illustrating the middle or large-sized battery pack having the battery module mounted in the middle or large-sized battery pack case of FIG. 1.
Referring to these drawings, a middle or large-sized battery pack 100 includes a battery module 32 configured to have a structure in which a plurality of unit cells 30 is stacked so that the unit cells 30 are electrically connected to each other, a battery pack case 70 in which the battery module 32 is mounted, a coolant introduction part 40, as a flow space, extending from a coolant inlet port 10 to the battery module 32 and a coolant discharge part 50, as another flow space, extending from the battery module 32 to a coolant outlet port 20.
A coolant, introduced through the coolant inlet port 10, flows through the coolant introduction part 40 and flow channels 60 defined between the respective unit cells 30. At this time, the coolant cools the battery cells 30. After that, the coolant flows through the coolant discharge part 50 and is then discharged out of the battery pack case through the coolant outlet port 20.
The coolant introduction part 40 is formed in parallel to the direction in which the unit cells 30 are stacked. In the above structure, a relatively high coolant flux is introduced into the flow channels defined between the unit cells adjacent to the coolant outlet port 20, whereas a relatively low coolant flux is introduced into the flow channels defined between the unit cells adjacent to the coolant inlet port 10, with the result that the cooling of the unit cells 30 is not uniformly achieved, and therefore, the temperature deviation between the unit cells adjacent to the coolant outlet port 20 and the unit cells adjacent to the coolant inlet port 10 is very high. This phenomenon occurs because the coolant concentrates on the coolant outlet port 20 side with the result that the temperature of the coolant inlet port 10 side increases.
Also, FIG. 3 is a vertical sectional view typically illustrating a middle or large-sized battery pack configured to have a structure in which a battery module is mounted in another conventional middle or large-sized battery pack case.
A middle or large-sized battery pack 100a of FIG. 3 is substantially identical to the middle or large-sized battery pack 100 of FIG. 1 in connection with the unit cells 30, the battery module 32, the coolant discharge part 50 and the flow channels 60. However, the middle or large-sized battery pack 100a of FIG. 3 is different from the middle or large-sized battery pack 100 of FIG. 1 in that a coolant inlet port 10a and a coolant introduction part 40a are inclined at a predetermined angle to a battery pack case 70a. That is, an upper end inside 42a of the coolant introduction part 40a is inclined at a predetermined angle toward an end of the battery pack case 70 opposite to the coolant inlet port 10a. Also, the end of the battery pack case 70 opposite to the coolant inlet port 10a is spaced apart from the top of the battery module 32 by a height H of approximately 1 mm so that the temperature of a coolant flowing between the unit cells 30 is uniform.
In this structure, the efficiency of cooling the unit cells 30 adjacent to the coolant inlet port 10a is relatively high as compared with the middle or large-sized battery pack 100 of FIG. 1. However, considerably high temperature difference still exists. In addition, the upper end inside of the coolant introduction part 40a comes into contact with the tops of the unit cells during vibration of the middle or large-sized battery pack 100a with the result that noise may be generated from the middle or large-sized battery pack or the middle or large-sized battery pack may be damaged.
Consequently, there is a high necessity for a technology to fundamentally solve the above-mentioned problems.